In terms of insulated foam sheathing, I am not sure which one would be best for this project. Should I use boards that contain laminated facers on both sides, on one side, or neither, just unfaced? Should I use XPS, EPS, or Polyiso?

I would recommend spray foam for the entire garage ceiling. It fills the cracks, provides a sealed vapor barrier and is fast. After that, suit yourself as to drywall choice. Thicker provides better sound attenuation.

You may not want to use greenboard for your ceiling in the main part of your bathroom. I don't believe it is rated for horizontal application, that is what i've read anyways. Apparently it does not have the same holding strength overhead for 16'' centres, you may be ok to go with furring strips at 12''oc if you are set on greenboard on the ceiling.

You may not want to use greenboard for your ceiling in the main part of your bathroom. I don't believe it is rated for horizontal application, that is what i've read anyways. Apparently it does not have the same holding strength overhead for 16'' centres, you may be ok to go with furring strips at 12''oc if you are set on greenboard on the ceiling.

Oh I thought green board was fine for ceilings?!?... How about purple board? I cant imagine using regular for any bath unless it doesn't have shower....

Perma wash has a good mold proof paint.

I don't believe it is, although I have used it myself in small amounts over showers and whatnot. This is just something i've read online, however it seemed true.

I would never use green board in a "wet area" as in a tiled area around a shower. However I do believe that reguar drywall , providing the ventilation is proper and a good paint is used, will be fine in non wet areas of the bathroom. Although I do use green board quite a bit in bathrooms, I have taken apart many bathrooms with regular drywall (in non wet areas) and no issues whatsoever.

Anyways I would look into it on the web/ consult with the manufacturer. I believe I read on a contractors website that it is not rated for ceilings, and cannot support its own height hung from a ceiling. As to whether this would apply to the purple board I would assume so, but not saying for sure.

I don't believe it is, although I have used it myself in small amounts over showers and whatnot. This is just something i've read online, however it seemed true.

I would never use green board in a "wet area" as in a tiled area around a shower. However I do believe that reguar drywall , providing the ventilation is proper and a good paint is used, will be fine in non wet areas of the bathroom. Although I do use green board quite a bit in bathrooms, I have taken apart many bathrooms with regular drywall (in non wet areas) and no issues whatsoever.

Anyways I would look into it on the web/ consult with the manufacturer. I believe I read on a contractors website that it is not rated for ceilings, and cannot support its own height hung from a ceiling. As to whether this would apply to the purple board I would assume so, but not saying for sure.

Yeah I haven't used purple board in any bathrooms I have done yet mostly green
I did a kitchen today and used green because I ran out of the white lol